A class of machines exists in the art generally known as “scroll” apparatus for the displacement of various types of fluids. Such apparatus may be configured as an expander, a displacement engine, a pump, a compressor, etc., and many features of the present invention are applicable to any one of these machines. For purposes of illustration, however, the disclosed embodiments are in the form of a hermetic refrigerant compressor.
Generally speaking, a scroll apparatus comprises two spiral scroll wraps of similar configuration, each mounted on a separate end plate to define a scroll member. The two scroll members are interfitted together with one of the scroll wraps being rotationally displaced 180 from the other. The apparatus operates by orbiting one scroll member (the “orbiting scroll”) with respect to the other scroll member (the “fixed scroll” or “non-orbiting scroll”) to make moving line contacts between the flanks of the respective wraps, defining moving isolated crescent-shaped pockets of fluid. The spirals are commonly formed as involutes of a circle, and ideally there is no relative rotation between the scroll members during operation; i.e., the motion is purely curvilinear translation (i.e., no rotation of any line in the body). The fluid pockets carry the fluid to be handled from a first zone in the scroll apparatus where a fluid inlet is provided, to a second zone in the apparatus where a fluid outlet is provided. The volume of a sealed pocket changes as it moves from the first zone to the second zone. At any one instant in time, there will be at least one pair of sealed pockets; and when there are several pairs of sealed pockets at one, each pair will have different volumes. In a compressor, the second zone is at a higher pressure than the first zone and is physically located centrally in the apparatus, the first zone being located at the outer periphery of the apparatus.
Two types of contacts define the fluid pockets formed between the scroll members: axially extending tangential line contacts between the spiral faces or flanks of the wraps caused by radial forces (“flank sealing”), and area contacts caused by axial forces between the plane edge surfaces (the “tips”) of each wrap and the opposite end plate (“tip sealing”). For high efficiency, good sealing must be achieved for both types of contacts.
The concept of a scroll-type apparatus has, thus, been known for some time and has been recognized as having distinct advantages. For example, scroll machines have high isentropic and volumetric efficiency, and, hence, are relatively small and lightweight for a given capacity. They are quieter and more vibration-free than many compressors because they do not use large reciprocating parts (e.g., pistons, connecting rods, etc.), and because all fluid flow is in one direction with simultaneous compression in plural opposed pockets, there are less pressure-created vibrations. Such machines also tend to have high reliability and durability because of the relatively few moving parts utilized, the relatively low velocity of movement between the scrolls, and an inherent forgiveness to fluid contamination.
The orbiting of the one scroll member with respect to the other scroll member creates an imbalance which is typically counteracted using one or more counterweights. When designing new compressors and/or redesigning and modifying existing compressors, it is sometimes necessary to design a new counterweight. The need for a new counterweight is typically required when the mass of the counterweight needs to be optimized for a specific application. Each time a new counterweight of a new mass is required, new molds for the counterweight of the specific mass must be developed. The development of the new molds incurs development time and capital costs associated with the new mold.
The present invention provides the art with a counterweight which includes a recess. The size and/or depth of the recess can be varied to vary the mass of the counterweight. Thus, a counterweight having common outer dimensions can be manufactured in various masses by changing the size and/or depth of the recess in the counterweight to meet the required mass for the counterweight. The fact that counterweights having different masses can still maintain common outer dimensions eliminates the need for the tooling on the assembly line which assemble the counterweights to the compressor assembly to be modified and/or changed when different masses of counterweights are used.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.